High voltage bushings are commonly used to carry current at a high potential through a grounded barrier.
Specifically, high voltage bushings are used to carry current from utility generators to the outside world. High voltage bushings typically comprise an inner conducting core to carry the current created within the generator to another location. The inner conducting core is typically housed by an outer insulating housing. Utility generators typically have hydrogen gas in them. The channel created by the high voltage bushing to the outside world creates a potential for leakage of the hydrogen gas to the environment external to the generator. Hydrogen gas is extremely flammable and explosive in some environments.
High voltage bushings are typically fitted with a flange that surrounds the outer insulating housing. The flange may be used to secure the high voltage bushing in place and seal the gap between two environments. The interior surface of the flange may be used to seal the gap between the internal operating environment of the generator and the environment external to the generator.